The present invention relates to digital data communications systems and more particularly to such a system which flexibly accommodates terminals of different throughput capabilities.
The prior art encompasses a wide variety of schemes for encoding and multiplexing digital data streams for communication between terminals. These schemes include frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). Further, some systems have been devised which utilize various combinations of FDMA, TDMA and CDMA.
One problem with known prior art systems, however, is that they do not readily accommodate terminals of differing throughput capabilities in an integrated digital network. In particular, data communication systems utilizing satellite relay typically expect or require that all terminals interconnected in the network will have similar throughput capabilities and will utilize a common encoding and multiplexing scheme. Conventional communication systems (digital or not) using FDMA and satellite relay, or any other form of radio relay, can accommodate multiple isolated point-to-point channels of differing throughput in configurations normally referred as stove-pipe architectures, where integrated digital networking is not possible. Conventional communication systems using TDMA and satellite, or any other form of radio relay, cannot accommodate terminal transmitting at significantly different burst rates, requiring all the terminals to use antennas of approximately same diameter, TDMA systems that make use of variable-rate burst modems can accommodate channels of differing throughputs, but it does so by making very inefficient utilization of equipment at sites with relatively larger antenna diameters, where a great number of modems is required to handle communications with disadvantaged terminals. Conventional communication systems using CDMA and satellite, or any other form of radio relay, typically cannot handle reception of signals at varying power levels from different terminals, a problem normally referred as the "near-far-problem. "
Among the several objects of the present invention may be noted the provision of a method and system for providing digital data communications between terminals of differing throughput capabilities; the provision of such a system in which terminals of different throughput capabilities can utilize a satellite or radio relay; the provision of such a system which efficiently utilizes the throughput capabilities of terminals of different throughput capacities; the provision of such a system which can flexibly allocate channel bandwidth and terminal transmission power in accordance with data traffic needs; the provision of such a system which can be straightforwardly implemented; the provision of such system high throughput terminals can support a number of low-throughput terminals with a single or minimum number of modem units; the provision of such a system which does not require unique components; the provision of such a system which is highly reliable and which is of relatively simple and inexpensive implementation. Other objects and features will be in part apparent and in part pointed out hereinafter.